1. Field of the Invention:
The present invention relates generally to an improved method of hydrostatic extrusion of compound billets composed of more than two different metallic materials and, more particularly, to an improved method of obtaining stable and satisfactory products covering an extremely wide selection of combinations of different metallic materials as well as the shapes thereof.
2. Description of the Prior Art:
It is known, as disclosed in U.S. Pat. No. 3,620,059, that a compound billet may be formed by hydrostatically extruding an internal material and an external material, each one being of more than two different materials.
However, even in the case of effecting a hydrostatic extrusion by employing a sealed billet, as hereinbefore mentioned, there are still a number of problems to be solved. For instance, in the event there is a great difference between the deformation resistance of the different metallic materials, satisfactory products will not be obtained due to the fact that surface slip will take place at the contact plane of the different materials and further due to the fact that such surface slip will be intermittent, whereby wave-shaped irregularities occur on the products and sometimes at least one of the different metallic materials is thereby destroyed.
Further, surface slip of the different metallic materials is not only due to the difference between the deformation resistance of the different metallic materials, but is also affected by the compatibility of the different metallic materials, the degree of cleanliness of the surfaces thereof, the contact pressure at the time of deformation, and the like. Therefore, in order to manufacture products whose range enables a free and wide selection of combinations of different metallic materials and the shapes thereof, a solution of the problems has been difficult within the framework of complex conditions caused by the instability due to the aforementioned surface slip and intermittent surface slip phenomena.